The present invention is directed to an improved method and apparatus to separate solids particles from a liquid medium and/or classify suspensions of particles according to particle characteristics by centrifugal force, wherein the feed stream is introduced to the cyclone apparatus at a location along the central internal axis of the cyclone.
Cyclones are in wide use throughout the solids processing industries. Cyclones are commonly used to separate solids from a liquid medium and/or to classify suspensions of particles according to particle characteristics. A typical cyclone will be described for purposes of generally describing the prior art with reference to FIG. 1.
A typical prior art cyclone consists of a cylindrical shell 1 to which is joined at the bottom orifice an inverted conical shell 2. The cone angle of the inverted conical shell 2 may be constant or variable, and the cone may be curved rather than linear. One widely used cyclone, patented by Visman (U.S. Pat. No. 3,353,673), has an inverted conical shell consisting of three conical segments, each with a different slope. The cylindrical shell 1 is closed at the top. The inverted conical shell 2 is truncated and open at the bottom. The bottom opening is commonly known as the underflow nozzle or apex orifice 3. It will be understood by those skilled in the art that the designations "top" and "bottom" do not necessarily designate or restrict the cyclone's spatial orientation, as the cyclone may be operated with its central axis oriented vertically, horizontally, or on an inclined angle.
Cyclones with elongated conical shells (i.e., a shallow conical angle) are often referred to as "thickening" cyclones, and are more useful in the concentration of very fine particles. Cyclones that have a relatively moderate cone angle and thus an inverted conical shell of medium length are known as "heavy media" cyclones and are most useful in separating particles according to particulate characteristics. Cyclones with an extremely sharp cone angle and therefore a particularly short inverted conical shell are known as "hydrocyclones" and are typically used to remove heavy solids particles from the feed mixture. The Visman tricone described above is a type of hydrocyclone.
A vortex finder 4, also known as an overflow nozzle, is centrally mounted along the internal axis of the cyclone. The vortex finder 4 extends through the top of the cylindrical shell 1 into the interior of the cyclone, terminating near the juncture of the cylindrical shell 1 and the inverted conical shell 2.
The feed stream, consisting of the particulate material and its entraining liquid, is delivered to the cyclone under pressure, and is introduced to the cyclone through a feed nozzle 5 at the wall of the cylindrical shell 1.
The entering material forms characteristic whirling movement patterns whereby it separates into two rotating streams. The movement patterns have been described elsewhere, for example by Tomlinson (U.S. Pat. No. 3,096,075). An air core forms along the central internal axis from the apex orifice 3 upward into the vortex finder 4. Heavy particles, and/or smaller particles of relatively higher specific gravity, tend to spiral downward along the inner wall of the inverted cylindrical shell 1 toward, and ultimately exiting through, the apex orifice 3. The liquid, containing smaller lighter solids particles, forms a vortex pattern swirling and spiraling upward around the air core and into the bottom of the vortex finder 4.
Inside a cyclone in which the pattern of material separation has been formed and defined, the incoming pressurized feed stream merges with the mass of material that is spiralling downward toward the apex nozzle. The feed stream is introduced near the outermost edge of the downwardly rotating mass, where the centrifugal force of the rotating mass is lowest. Prior art cyclones typically exhibit severe wear of the interior wall of the cyclone near the feed nozzle.